… which was really ripe for DRYing up. The problem was that the partial would need to accept a parameter of some sort (for the category name). The official Liquid documentation leaves much to be desired, but there’s a tiny part in the Templates section of the Jekyll documentation that saved the day:

You can also pass parameters to an include. Omit the quotation marks to send a variable’s value. Liquid curly brackets should not be used here: